1. Field Of The Invention
The present invention relates to substantially solvent-free asphalt-based materials. More specifically, the present invention is directed to the use of fatty acids and derivatives thereof to substantially eliminate the need for solvent in asphaltic adhesives, sealants and the like.
2. Discussion Of The Prior Art
Asphalt is a dark, cementitious material having a solid or semi-solid consistency. It occurs naturally or as a petroleum derivative and is generally composed primarily of bitumens--generally paraffinic and aromatic hydrocarbons and heterocyclic compounds containing sulfur, nitrogen, and oxygen.
Asphalt is relatively inexpensive and has a relatively high penetration value when applied to most porous surfaces. Furthermore, asphalt is relatively weather resistant and water impermeable. As a result, asphalts have traditionally been used as protective films, adhesives, binders, and the like.
Asphalt can be used in a variety of forms, such as blends or emulsions, and can be processed by a variety of known techniques. Consequently, a large variety of asphalt based products can be found on the market, and are used in: paving; roofing; joint sealing; specialty paints; electrical laminates; hot melt adhesives; low-grade rubber product dilutents; radioactive waste disposal dilutents; hot-dip coatings; and water retention barriers.
A class of asphalt compounds are known generally which flow or are otherwise easily spread over a surface and which cure to a rubbery, elastomeric consistency. Such asphalt compounds, particularly cold applied asphalt compound, required the use of solvents to keep the asphalt component intermixed with other required components, such as elastomeric polymers, prepolymers and/or the like. Examples of other such required components would include isocyanate, styrene-butadiene and/or polybutadiene based elastomers and prepolymers thereof.
To aid in the mixing of asphalt with other otherwise non-miscible compounds, organic solvents have generally been used, such as toluene, aromatic oils, naptha, mineral spirits or carbon disulfide. Such solvents will suspend the asphalt into a dispersion and allow the other components to intermix with the asphalt. After mixing, the mixture can be easily applied by conventional technology. Thereafter, the solvent will evaporate off, leaving the asphalt properly intermixed with the other constituents.
However, solvent systems are being criticized by environmentalists and environmental government agencies. Solvents used in asphalt systems are generally deemed harmful to the environment if present above certain levels. Furthermore, persons handling the asphalt system risk exposure to these potentially harmful solvents. As a result, government regulations have become increasingly restrictive concerning volatile organic content ("VOC") of materials.
Solvent in asphaltic compounds can also cause other problems, such as an undesirable increase in viscosity, particularly at lower temperatures (indeed, many asphaltic systems cannot be applied much below 20.degree. C). High viscosity can also make an adhesive difficult to pour, pump or apply.
Yet another problem with solvent based adhesives is the potential for blister formation, particularly when a second coating is placed over the solvent based adhesive. If too little solvent is able to escape, the solvent vapors can accumulate and cause the coating to blister. On the other hand if the solvent is able to escape too freely, the adhesive may "dry up", pull away, or crack due to the rapid loss of solvent.
Furthermore solvents can increase the cost of the adhesive, due to increased shipping costs, handling costs and the like. Such solvents can also increase the flammability of the substance, and may cause unwanted side reactions.
Moreover, many solvent based systems provide poor green strength--that is, they are not sufficiently tacky (due to the presence of solvent) to provide adequate bonding and/or adhesion immediately upon application and prior to complete or substantial curing. Without substantial green strength, clamps, supports and the like must be used substantially during the time the material cures.
As a result, a tremendous need exists and has existed for many years for solvent-free asphaltic systems. Substantial research has been done in the industry to find a way to eliminate the need for asphalt solvents. However, for one reason or another, the industry has had to continue using asphalt solvents, much to the consternation of numerous government agencies, environmentalists and other concerned citizens.